1. Field of the Invention
The present invention relates to an improved seal for a piston pump and more particularly, relates to a self-threading seal for sealing a pliant deformable tube to a cylindrical shaft.
2. Background Information
An improved pump that uses the type of seal of this invention is disclosed and described in U.S. Pat. No. 5,415,531 to Cavanaugh dated May 16, 1995, which is an improvement to a pump assembly of the general type disclosed and described in U.S. Pat. No. 5,094,596 of Erwin, Cavanaugh and Hetherington issued in March 1992. The pump of the '531 patent provides a new combination of structural features that together produce an enhanced operational performance. This patent describes a pump assembly that has a dynamic block and output block defining a dynamic chamber and pumping chamber respectively. The dynamic block abuts the output block such that cylindrical peripheral wall of the dynamic chamber is coaxial with, and substantially the same diameter as the cylindrical peripheral wall of the pumping chamber.
The pump assemblies of this patent is comprised of a pair of opposing single-acting, piston pumps operating alternately by means of an interposed actuator such as a fluid actuating air motor isolated from the fluent material by an actuating seal. An annular seal is clamped between the outlet block and the dynamic block on either side of the pump, and extends radially inwardly into engagement with the periphery of the piston. The annular seal is in continuous engagement with the periphery of the piston, and remains spaced from all other surfaces within the pump to minimize wear.
The piston rod is provided with annular grooves that are positioned within the dynamic chambers on either side of the pump. The articulating seal is a movable seal member, preferably a bellows seal, sealingly engaged in the annular grooves of the piston rod. A second end of the articulating movable seal member, sealingly engages the dynamic chamber end wall. An isolation chamber, located between the dynamic chamber and seal assembly of the actuator, isolates and drains away any motor fluid such as air or hydraulic fluid, which might pass through the seal assembly.
The articulating movable sealing member isolates the dynamic chambers from the actuator and the interior of the seal is vented via the isolation chamber so the seal may move without restriction. That is, the bellows seal may readily expand and contract. The seal member thereby, seals the piston rod to the side of the chamber and end wall and creates a sealed dynamic chamber.
The articulate bellows seal of the patent has a cylindrical end having an inner diameter equal to the outer diameter of the piston rod, and positioned about the rod to overlay a pair of annular grooves formed in the circumference of the rod. A clamp, such as a base clamp, is provided to clamp the tubular .cylindrical end of the seal around the piston rod. The annular grooves are formed in the circumference of the piston rod to be in the dynamic chamber. The cylindrical end of the bellows seal, positioned about the annular grooves, is partially forced into the grooves by the clamp to fixedly secure the cylindrical end to the piston rod providing a seal.
However, a problem with the seal provided between the tubular cylindrical end of the bellows seal and the hose clamp is that after periods of use, the hose clamp can become loose causing the seal to fail and requiring maintenance of the pump. This maintenance occurs much too frequent and requires replacement of the clamp and seal to correct the problem. It would be advantageous if a seal could be provided that would not deteriorate over a long period of use.
Therefore, it is one object of the present invention to provide an improved seal.
Yet another object of the present invention is to provide an improved seal between a cylindrical shaft and a pliant tubular member.
Still another object of the present invention is to provide an improved method of sealing a pliant tubular member against a cylindrical shaft.
Yet another object of the present invention is to provide an improved seal for an articulating seal in a pump.
Still another object of the present invention is to provide an improved seal between a reciprocating piston rod and an articulating seal having a pliant tubular end.
Yet another object of the present invention is to provide an improved seal between a reciprocating piston rod having a plurality of circumferential grooves, and an articulating seal having a pliant tubular end positioned over the plurality of circumferential grooves and set by a self-threading member.
Yet another object of the present invention is to provide an improved seal between a reciprocating piston rod having a pair of circumferential grooves, and an articulating seal having a pliant tubular end by threading a coarse self-threaded nut over the pliant tubular end to deform the pliant tubular end into the circumferential grooves.